Automatic transmissions are usually equipped with a starter interlock system. This serves the purpose that a vehicle can only be started when a selector lever, actuatable by the driver, is in neutral or parking position. Starting the vehicle in a driving position, e.g. R or D, is hereby prevented. Such a starter interlock system has the following units: ignition lock, starting relay, selector lever, electric position switch and an electronic transmission control system. The electric position switch coverts the position of the selector lever into electrical signals. In practice, this can be obtained by situating the position switch on a rotatable shaft and the position switch having inside several conductor tracks with sliding contacts or working without contact. The output signals of the electric position switch represents in coded form, e.g. as 4-bit code, the position of the selector lever. The signals are then passed to the electronic transmission control system. Two contacts are also integral parts of the position switch. The first contact serves to control the reverse drive headlights when the driver has introduced the position R via the selector lever. The second contact serves to control the starting operation. This contact can be designed as closing switch, i.e. when the selector lever is in position P or N, said mechanical contact is closed. In this position, a current path exists from the supply potential to the reference potential, via ignition lock, starter relay and closed position switch. The vehicle can be started.
The above described starter interlock system has been disclosed, e.g. in the book "Automatische Fahrzeuggetriebe," H. J. Forster, Springer Verlage, 1991, pages 344 to 347. The electric design of the position switch is known from the same book, FIG. 10.48 on page 392.
A new trend of development in automatic transmissions now moves toward reducing the interfaces of the automatic transmission and moving the electronics to the interior of the transmission. This development is known by the technical expression "Elektronik vor Ort" or "Mechatronik."